(1) Field of the Invention
The invention relates to an elastomeric bush or plain bearing with a changeable radial rigidity or stiffness. The bearing can be switched between a state with a rather low stiffness and a state with a comparatively higher stiffness. The bearing consists substantially of a preferably tubular metallic inner part, a cylindrical outer part and an elastomeric bearing body arranged between the inner part and the outer part and connected at least with the inner part by vulcanization, and a bearing sleeve receiving the aforementioned elements of the bearing. At least two chambers for receiving a fluid are arranged in the bearing body.
(2) Description of Related Art
Elastomeric bush bearings are widely employed in particular in the automotive industry and are preferably used for supporting parts of the chassis. With respect to the driving comfort, high demands are placed on the bearing because they should keep away vibrations caused by uneven road surfaces from the passenger compartment and also insulate the passenger compartment to the greatest possible extent from noise originating from the vehicle units. Because of these resilient and damping characteristics, the bearings are of great importance and should also offer the largest possible degree of safety in dangerous situations as well as support the elasto-kinematics.
Because both low-frequency oscillations caused by uneven road surfaces and high-frequency acoustic vibrations caused by the vehicle units need to be effectively attenuated, the properties of the bearing can be adapted to different requirements by varying the geometry and the hardness of the elasticity of the bearing body (generally rubber). The passive embodiments of the bearings currently most widely used in series production attempt to achieve a compromise for attenuating vibrations of different frequencies. However, a more advantageous approach is to construct the bearings actively, i.e., to make it possible to switch the stiffness characteristic using suitable constructive measures for an automatic adaptation to the corresponding driving and road situation, based on various information from the vehicle.
In a possible approach for switching the stiffness of conventional bush bearings, the bearings are forcefully constricted in the axial direction to achieve the transition into a state of high stiffness. To this end, the bearing geometry, in particular the bearing body, is acted on by applying suitable electric or hydraulic means in the axial direction. Bush bearings of the aforedescribed type are described, for example, in DE 10 2006 040 958 A1 and DE 10 100 49 140 A1. Another possibility is to reduce the clearance of the bearing in the operating direction and to thereby temporarily increase the stiffness. For example, electric switching means are employed for this purpose, with corresponding examples disclosed in DE 10 2005 028 563 A1 and DE 103 30 877 A1.
The bearings constructed according to the aforementioned documents require comparatively high power for switching their stiffness characteristic, because the bearing must always be moved to a defined position when changing the stiffness, independent of its actual orientation or position.
The power required for switching the stiffness can be lowered with embodiments of elastomeric bearings that deviate from the basic principle where the bearing is secured in a predetermined position. This is achieved with bearings having at least two chambers that are filled with a fluid and connected with one another by a channel. The stiffness can be switched by alternatingly allow or prohibit fluid exchange between the chambers. Due to the incompressibility of the fluid, a high radial stiffness is produced in the region of a chamber filled with the fluid while fluid exchange is blocked, whereas the radial stiffness in the region of the other chambers emptied of the fluid is small due to the elasticity of the elastomeric bearing body or the rubber, respectively.
Several documents of the state-of-the-art disclose that the viscosity of the fluid may be changed during the switching process by alternatingly allowing or suppressing a fluid exchange between two chambers. For example, DE 39 10 447 A1 describes a solution where the fluid is an electro-rheological fluid whose viscosity is changed by suitable switching processes with electrodes projecting into the damping means or into the chambers receiving the damping means. As another possibility described, for example, in EP 1 705 400 A1 a magneto-rheological fluid can be used by changing its viscosity by applying different magnetic fields to the fluid. In the aforementioned solutions, the described stiffening mechanisms typically operate in parallel with the stiffness of the bearing body and the support body, respectively. However, the same effect could also be realized with a series connection. The latter solutions mentioned above are all based on a common principle to increase the stiffness by preventing the movement of the elastomer forming the bearing body by way of the incompressibility of the damping means and the fluid, respectively. Disadvantageously, very high pressures build up in the damping means chambers, which adversely affect the durability of the bearings.
It is an object of the invention to provide an alternative solution for an elastomeric bush bearing having a switchable stiffness. The intent is to obviate the aforementioned disadvantages of the state-of-the-art by designing the bearing so as to require neither high power for ensuring its switchability, nor adversely affecting its endurance by high stress on its elements.